Combustion device for solid fuels rich in gases



Jan. 9, 1945. P. A. ASTRADSSON 2,367,165

COMBUSTION DEVICE FOR SOLID FUELS RICH IN GASES Filed. Nov. 12. 1942 I v INVENTOR Patented Jan. 9, 1945 COUNIBUSTION DEVICELFOR some FUELS men IN GASES Per Anton fistradsson', Stockholm, Sweden ApplicationNovember' 12, 1942, Serial No. 465,364

- In Sweden October '2, 1941 p y 3 claims. (01. 235 -95) This invention relates to a combustion device for solid. fuelv rich in: gases and more particularly to a;thermostatic. regulating device for re ulating the admission of secondary air independence of the temperature: of thecombustion 5 if the quantity of gas decreases, the excess of gases. 2 i air will increase- Further, if the excess of air Incombustion of solid fuels richin gases, the increases, the temperature of the combustion combustion air is generally conveyed partly. to gases decreases. The means by which the reguthe solid fuel (primary combustion air) and part--, lation of the air supply is attained according to ly to the. gases escaping from the burning fuel the present invention, must thus influence'the (secondary combustion air). The amount of supply of air in such a way as to restore the combustible gases generated from the fuel mainoriginal excess of air, that is a decrease of the 1y depends on the production of heat from the air supply. For'this purpose the combustion delayer of fuel, and a certain regulation of the vice according to the present invention is proproduction of gas in the furnace is. therefore vided with a thermostatic device so arranged as possible by regulating the primary air supply. to reduce the quantity of secondary air at a There is some lag, however; sothat the generadecreasing temperature of the combustion gases. tion of gas goes on even after the: primary air It is also possible to use this thermostatic device supply has been. shut. off. Since the reactionsin for the purpose of regulating the primary air the generation of. gas are chiefly exothermic, the 0 supply in an ordinary way, so that this increases disaggregation of the fuel might even go on unwhen the temperature of, the combustion gases til entirely completed. These circumstances decreases. make the regulation of, the: combustion device 'In the following the invention will be more difficult. If, for instance, the combustion device fully described with'reference to the accompanyis continuously burning witha combustion correing drawing, diagrammatically illustrating two sponding to a certain heat requirement and a embodiments. reduced productionof heat is required, this can- Fig. 1 is a cross section of a cooking stove, not be. carried out without difiiculties. If the fragmentarily shown. supplyof primary and secondaryair is reduced Fig. 2 is a similar cross section as Fig. 1 but in proportion to the. reduced heat requirement, with modified air regulating means. then the amountof air supplied will not be suiii- Fig. Sis the air regulating details in side view. cient. for a completecom-bustion of the fuel gases In Fig. 1, the fuel chamber I of the stove is whi h mi ht still be produced. n t e same provided atthe bottom with a grate 2. The m ton the other hand, n P gases generated from the fuelleave the fuely air pp y is reduced and the Secondary chamber at its bottom part and pass into a flue 3 p is unaltered, conditions for Combusleading to a chimney. When entering into this W111 be Suitable to begin with, but i flue, the gases meet secondary air which is sucked production of, gas is, gradually reduced there. will in draft through an l t 4, an ash pit 5, be an excess of air and consequently anincrease and the grate 2' m g losses In order, always 9 40 Primary air is supplied to the fuel chamber in 1 a cqmbustlon condmonsnthe i its upper part througha duct 6, in which is arv if; 5 must beiregul'a'ted m ranged a damper 1. The inlet a of the duct 5 is -gent -way. This, however, means skilled Y situated 1n front of the inlet 4. A thermostatlc people for attendance and care. of. the combusd f 11 k com f B tion deviceand expensive.- apparatus for control-- evlce 0 nown ype 1S pose o o 1mg the firing I don tube 9 connected to a receptacle I I by means The. present invention refers to simple means of f f e parts form, a closed system for an automatic regulation of the secondaryair fzonta'mmg fluld' The receptacle H is located supply, so that such air will always'be supplied m the flue The free end of the Bourdon in, suitablequantities; The v t is based springv tube carries two valve. discs l2 and I3, on the idea of letting a tendency to alteration located in from of t e Secondary and primary ofth excess. r give an impulse, t the airv inlets 4 and 8, respectively. The thermo-- regulating members: to the effect th t: thi alstatic device is arranged between. the air inlets teration is.-counteracted. practice there is 4 and 8 in such a way that; When Boul'don alwayssome excem. of air.-; Ari alteration'of the quantity of gas escaping from the fuel, entails, at a constant supply of air, an alteration of the excess of air. If the quantity of gas increases,

the excess of air will decrease, and conversely,

spring tube expands, the valvediso l2 withdraws from the secondary air inlet 4 while the valve disc I3 approaches the primary air inlet 8.

The upper parts of the fuel chamber and the flue 3 are arranged in good heat-conducting connection with a hot plate I5. On the other hand, the bottom part of the fuel chamber should be in poor heat-conducting connection with the hot plate, or even surrounded by heat insulation, thus making it possible to maintain combustion in the bottom part of the fuel chamber with slight losses when the stove is idle. For this purpose, the grate 2 is arranged in such a way, that the secondary air also touches the fuel that is lying on the grate in the bottom part of the fuel chamber and which has evolved its gas. Further, a special opening I4 is arranged in the ash pit wall for the supply of a slight volume of secondary air even when the valve disc I 2 completely closes the inlet 4.

When the stove is cold, the valve disc I2 is in the latter position that is, closing inlet 4. When lighting a fire in the stove, fuel, such as wood, is put in the fuel chamber and the damper I should be opened. When the fuel has been ignited, combustion is first sustained by the primary air entering through the inlet 6 and the slight amount of secondary air that enters through the opening I4. When the combustion gases have reached a certain temperature, the

valve disc I2 is, however, moved by the thermostat from the orifice of the inlet 4, so that plenty of secondary air is supplied. The valve disc I3, however, still leaves the inlet 8 almost entirely open so that also plenty of primary air enters. The combustion is then rapidly increased and the temperature in the flue 3 rises, actuating the thermostat so that the valve disc I3 gradually closes the primary air inlet 8. If the temperature in the flue 3 increases too much, the inlet 8 will be substantially closed, thus diminishing the combustion in the fuel chamber and also the generating of gas. By means of the thermostat, the combustion will thus be so regulated that a certain temperature is maintained in the flue 3. When the evolution of gas is nearly completed, the combustion, then mainly limited to the fuel chamber, is unable to maintain this temperature in the flue 3. The valve disc then gradually opens the inlet 8 for the primary air, and the combustion of the fuel, void of gas, increases. At the same time the valve disc I2 approaches the inlet 4, thus reducing the supply of secondary air in proportion to the reduced evolution of gas.

If more fresh fuel is supplied, the evolution of gas from the fuel commences immediately, a rapid combustion of gases takes place again in the flue 3, and the temperature there will rise considerably. The thermostat will then again limit the supply of primary air to the value necessary for maintaining normal temperature in the flue 3, simultaneously increasing the supply of secondary air.

When the stove is no longer to be used, the

damper I should be shut, so that the supply of primary air ceases. Secondary air will, however, still be supplied to the full extent, and the gases formed in the fuel chamber will thus still be completely consumed. The evolution of gas ceases gradually, however, and the temperature in the flue 3.falls. The consequence of this is that the thermostat reduces the air supply through the inlet 4. It is suitable to adjust the thermostat in such a way that the valve disc I2 completely shuts the inlet 4 when the evolution of gas has completely or nearly ceased. Air will then only enter through the orifice I4 and to such an extent that it is only just suflicient'for maintaining combustion of the fuel in the bottom part in such a degree that the fuel is maintained at ignition temperature.

In the embodiment as shown in Figs. 2 and 3 the orifices of the inlets 4 and 6 face in the same direction and the valve discs I2 and I3 are supported by a thermostat rod [6. The Bourdon spring tube 9 is placed on a lever I1 journalled on a pin I8, which is fixed to one end of another lever I9, the other end of which is journalled on a bolt 20 firmly screwed into the stove. The free end of the lever I1 is urged by a spring 2| against an eccentric 22 and the said spring also presses the other lever I9 against an eccentric 23. The eccentrics 22 and 23 are firmly fixed to a turnable spindle 24, which may be turned by means of a handle 25 located on the outside of the stove to adjust the eccentrics. The dimensions of these eccentrics are such that when turning the eccentrics, the thermostat rod I6 and the valve discs I2 and I3 receive a parallel movement. By

' means of this construction an adjusting of the handle 25 alters the neutral position of the thermostat, that is the temperature at which the thermostat valve discs completely close the air inlets 4 and 6. This is impossible with the construction according to Fig. 1.

While I have shown my invention applied to a cooking stove, it is to be understood that this has been done for purposes of illustrating only, and that the scope of my invention is not to be limited thereby, but the invention is to be applicable to any combustion device.

What I claim is:

1. In a combustion device for burning solid fuels rich in gases, a combustion chamber, means for supplying primary air for supporting combustion of said solid fuel in said chamber, means for supplying secondary air for supporting combustion of gas evolved from said solid fuel, a flue for conveying products of combustion from said combustion chamber, and thermostatic means disposed in heat-exchange relation. to said products of combustion responsive to a given decrease in the temperature of said flue gases for decreasing the quantity of secondary air While maintaining the quantity of primary air substantially constant and responsive to an increase in said temperature for decreasing the quantity of primary air While maintaining the quantity of secondary air substantially constant.

2. In a combustion device for burning solid fuels rich in gases, a combustion chamber, means for supplying primary 'air for supporting combustion of said solid fuel in said chamber, means for supplying secondary air for supporting combustion of gas evolved from said solid fuel, a flue for conveying products of combustion from said combustion chamber, thermostatic means disposedin heat exchange relation to said products of combustion and a controller actuated by said thermostatic means to increase the flow of secondary air as the temperature of the products of combustion increases while maintaining maximum flow of primary air and to decrease the flow of primary air while maintaining the maximum flow of secondary air after a predetermined temperature of the products of combustion has been released.

3. In a combustion device for burning solid fuels rich in gases, a combustion chamber, means for supplying primary air for supporting combustion of said solid fuel in said chamber, means for supplying secondary air for supporting combuscombustion chamber, thermostatic means disposed in heat exchangerelation to said products of combustion and a controller actuated by said thermostatic means to increase the flow of secondary air as the temperature of the products of combustion increaseswhile maintaining maximum flow of primary air and to decrease the flow 10 of primary air while maintainingthe maximum flow of secondary air after a predetermined temperature of the products of combustion has been reached, said means being further operable to simultaneously increase primary air flow and decrease secondary air flow and to simultaneously decrease primary air flow and increase secondary air flow;

PER ANTON ASTRADSSON. 

